The invention relates to an exhaust gas turbocharger for an internal combustion engine having a turbine with a housing including at least two inlet passages and a bypass channel extending from at least one of the turbine inlet passages and including a bypass valve to permit discharge of exhaust gases.
DE 29 01 041 discloses such an exhaust gas turbocharger with a turbine which has a rotor and a turbine casing with two inlet passages separated by a partition. A bypass passage, in which a bypass valve is arranged, branches off from one of the two inlet passages. By means of the bypass passage including the bypass valve, exhaust gas can be branched off from the turbine inlet passage and can be fed back into the exhaust gas line downstream of the turbine.
For the general technical background, reference is further made to the publications DE 42 35 794 C1, DE 35 28 225 A1, DE 29 41 704 C2 and DE 28 55 687 C2.
A problem of exhaust gas turbochargers lies in the fact that, for a long service life, critical temperature and pressure condition values must be maintained especially in the upper load range. So-called blow-off devices, for example, axial slide valves, represent a known remedy, by which the contour of the turbine casing can be changed in the region of the inlet-side rotor periphery and a partial flow of the exhaust gas past the turbine rotor is made possible. The turbine-side exhaust gas throughput can be suddenly increased in that a certain amount of exhaust gas is not conducted through the turbine rotor, where it would perform work, but rather is conducted past the rotor. For double flow exhaust gas turbochargers, two blow-off devices may be necessary for their reliable operation.
A further problem for turbocharged internal combustion engines, the supercharges of which are optimally configured with regard to consumption, is that, in relevant characteristic ranges of the internal combustion engine, the supercharging pressure is higher than the exhaust gas back pressure of the engine, and thus simple recycling of the exhaust gas to the in-take side of the internal combustion engine is not possible. In order, nevertheless, to be able to supply exhaust gas to the intake air stream so as to reduce the NO.sub.x emissions, the air flow downstream of the charge air compressor is in many cases again throttled down to a pressure below the exhaust gas back pressure using a throttle valve. Exhaust gas is not normally admitted upstream of the charge air compressor in order to avoid contamination of the compressor and also contamination of a downstream charge air cooler, since such contamination would result in a significantly reduced service life of these components.
It is the object of the invention to provide a two-or multi-flow exhaust gas turbocharger which is structurally simple and cost-effective and which permits a control of pressure in the various flow passages.